The present invention relates to an engine unit mounted on a motorcycle such as a scooter type vehicle or the like.
Generally, in an engine unit of a scooter type vehicle, a belt type transmission is integrally connected to a rear portion of an engine and a rear wheel is directly pivoted to a most rear portion of the transmission. A front portion of the engine unit is pivoted to a body frame of a motorcycle body and a rear portion thereof is suspended to the body frame by a shock absorber. Thus, whole of the engine unit is swung vertically together with the rear wheel so as to act as a part of a swing arm of the rear wheel.
According to the structure mentioned above, it is advantageous to increase a capacity of an article accommodation space placed above the engine unit and improve a riding quality by making hard an engine vibration to be transmitted to the frame side. However, on the contrary, since a weight of the whole of the engine unit becomes heavy in the case that a displacement (exhaust amount) of the engine is increased, a divided load of the rear wheel is increased, a load distribution between front and rear wheels is made improper and a support rigidity becomes low level, so that it is disadvantageous that a steering performance and a running stability are deteriorated.
Then, as shown in Japanese Patent Laid-Open Publication Nos. HEI 10-324287 and 11-129969, there have been developed a scooter type vehicle in which an engine and a transmission are fixed to a body frame side and only a shaft drive apparatus extending rearward from the transmission is made vertically swingable to drive the rear wheel. Accordingly, it is possible to mount an engine having a heavy load to a front side of the body frame as like as in the normal type motorcycle so as to make a load distribution between the front and rear wheels proper.
In the engine unit described in Japanese Patent Laid-Open Publication Nos. HEI 10-324287 and 11-129969, an engine case (a crankcase), to which the crankshaft and the counter shaft rotating with the crankshaft in an interlocking manner are pivoted, is separated in a direction of a vehicle width. Further, there is another engine unit of a motorcycle in which the engine case is separated in a vertical direction.
However, in the structure in which the engine case is separated in the direction of the vehicle width or the vertical direction, since face directions of respective mating faces (the separated surfaces) are different from a face direction of a mating face between the cylinder assembly and the engine case, it is necessary to machine a plurality of mating faces having different face directions in the engine case, so that as well as a lot of labor and time is required for machine working, it is very disadvantageous in view of accuracy.
Further, since a fastening member for assembling the engine case itself and a fastening member for fastening the cylinder assembly to the engine case are independently required, many numbers of the fastening members are required, and it is hence unavoidable that the number of the parts and much labor and time for assembling working are increased, thus increasing a manufacturing cost of the engine unit in addition to the hard machining of the engine case.
An object of the present invention is to substantially eliminate defects or disadvantages encountered in the prior art mentioned above and to provide an engine unit of a motorcycle capable of reducing a manufacturing cost of the engine unit, improving an assembling property and improving assembling accuracy of the engine unit by easily machining a cylinder block, a crankcase and the like and reducing a number of the parts, and improving a support rigidity of the crankshaft and a counter shaft pivoted in the engine unit.
Another object of the present invention is to provide an engine unit of a motorcycle capable of improving a layout of an exhaust muffler by making large a ground clearance below a cylinder head, improving an oil returning property of the cylinder head, increasing an oil storage amount and achieving easy attaching and detaching of an oil filter.
These and other objects can be achieved according to the present invention by providing an engine unit of a motorcycle comprising a cylinder head, a cylinder block formed with a cylinder bore therein, a crankcase and a rear case, which are sequentially assembled in this order from a front side of a motorcycle body, wherein a crankshaft is pivoted to a mating face between the cylinder block and the crankcase, a counter shaft which is rotated with the crankshaft in an interlocking manner is pivoted to a mating face between the crankcase and the rear case and these two mating faces lie in planes parallel to each other so as to be substantially perpendicular to a center axis of the cylinder bore of the cylinder block.
In a preferred embodiment, the cylinder block is fastened by a fastening member inserted from a side of the rear case so as to extend through the crankcase to thereby fasten the rear case and the crankcase together to the cylinder block in a clamped manner. The fastening member has a center axis parallel to the center axis of the cylinder bore. The fastening member includes a plurality of through bolts which are arranged in a vicinity of the crankshaft and the counter shaft so as to clamp the crankshaft and the counter shaft therebetween.
The cylinder head is fastened and fixed to the cylinder block by a plurality of long fixing bolts and a single short fixing bolt, and the crankcase and the rear case are fastened and fixed to the cylinder block by the four though bolts and a plurality of fixing bolts. All of these fixing bolts have center axes substantially parallel to the center axis of the cylinder bore.
The center axis of the cylinder bore is arranged so as to extend substantially along a longitudinal direction of the motorcycle body in a side view thereof and at least one of the cylinder block, the crankcase and the rear case has a lower portion lowered below a lower surface of the cylinder head so as to provide an inner portion of the lowered portion as an oil storage portion. The center axis of the cylinder bore has an front upward inclination in a side view of the motorcycle body and the oil storage portion has a bottom formed to be flat substantially in parallel to a road surface. The oil storage portion has a front portion to which an oil filter is placed below the cylinder bore in a side view of the motorcycle body and above the bottom of the oil storage portion.
According to the characters and structures of the engine unit of the motorcycle of the present invention mentioned above, it is easy to execute a flattening (plane) machining or working of the mating faces of the crankcase and the cylinder block, and the accuracy in parallelism between the respective mating faces can be improved. Further, in the case of making rectangular (right angle) a relative angle between the face directions of the respective mating faces and the center axis of the cylinder bore, since it is possible to continuously execute a flattening machining of the mating face of the cylinder block and a drilling working of the cylinder bore, it becomes further easy to work and it is hence possible to significantly increase a rectangular (vertical) accuracy of the center axis of the cylinder bore with respect to the mating face. Accordingly, a manufacturing cost of the engine unit can be reduced and the working performance can be also improved.
Furthermore, in accordance with the structure of the preferred embodiment mentioned above, the following advantages functions and/or effects will be attained.
Since the rear case and the crankcase can be fastened to the cylinder block by the common fastening member, it is possible to reduce the number of the fastening members, resulting in the manufacturing cost reducing and improvement of the assembling property. Further, since the long fastening member extending through the entire crankcase is utilized to be fastened to the cylinder block, it is possible to significantly increase a mounting rigidity of the crankcase with respect to the cylinder block.
Since it is possible to work an inserting hole of the fastening member at the same time of drilling working of the cylinder bore in the cylinder block, the assembling working can be significantly performed.
Furthermore, according to the location of a plurality of fastening members, i.e. through bolts, the support rigidity of the crankshaft and the counter shaft can be improved
Still furthermore, it is possible to omit an oil pan which is conventionally provided as an independent member below the crankcase or the like, whereby the number of the parts can be reduced, and since it becomes unnecessary to form an oil pan mating face in the crankcase, the assembling working can be easily done.
Still furthermore, the ground clearance below the cylinder head becomes large, a layout of the exhaust muffler can be improved, so that the oil supplied within the cylinder head can be easily returned to the oil storage portion, and it is also possible to increase the oil storage amount.
Still furthermore, it is possible to improve an attaching and detaching property of the oil filter.